Update headers on login screen

[saseestone]

In FOLIO circ subgroup demo, there was concern from Lane staff about use of "Stanford community" header for the SUNet ID option. Stanford Hospital staff feel part of the Stanford community, but they will need to use the "Library cardholder" option in requests.

We have explanatory text in the Library cardholder option helping Stanford Hospital staff remember that this is their path. But there was deep concern over the header text.

@dbranchini had some ideas immediately after the demo, but none that aren't problematic. We'll need to keep thinking on this.